Elenco Electronics EP-130, Manual, Page: 133 / 160

This project is a simple but effective code transmitter
like the kind used by military and amateur radio
operators around the world. When you press and
release the key, the transmitter turns on and off in
sequence.
You can use a common AM radio to receive the code
sent out by this transmitter. Tune the radio to a weak
station. The transmitter signal mixes with the station’s
signal to produce an audio tone called a beat note.
This beat note is what you hear as the code signal.
Use the tuning capacitor to tune this transmitter until
you can hear the beat note in the receiver when you
press the key.
You can receive the carrier wave (CW) signal of this
transmitter on a communications receiver, without
tuning to another station, if the communications
receiver has a beat frequency oscillator (BFO). The
BFO beats with your transmitter’s CW signal and
produces the tone.
This oscillator sends out an RF signal because the
frequency is very high (500,000Hz to 1,600,000Hz).
When you tune to a weak AM station first and then
send a signal slightly off from the station frequency,
you can hear the beat note that you produced.
Transmission and reception of CW signals is very
efficient. In fact, it is the most reliable type of
transmission for some emergencies. You might find
that you do not need an antenna, but if you do, 1, 2,
or 3 feet (about 60-90 cm) of wire will probably be
enough. Have fun!
Notes:
EXPERIMENT #112: WIRELESS CODE TRANSMITTER
-133-
Schematic
Wiring Sequence:
o
41-6-11-ANT
o
7-89-110-137
o
8-12-100
o
40-90-99
o
42-79
o
80-109-119
o
121-122
o
124-138